Shark Bay’s waters, islands and peninsulas....have a number of exceptional natural features, including one of the largest and most diverse seagrass beds in the world. However it is for its stromatolites (colonies of microbial mats that form hard, dome-shaped deposits which are said to be the oldest life forms on earth), that the property is most renowned. The property is also famous for its rich marine life including a large population of dugongs, and provides a refuge for a number of other globally threatened species.[1]

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The record of Australian Aboriginal occupation of Shark Bay extends to 22,000 years BP. At that time most of the area was dry land, rising sea levels flooding Shark Bay between 8,000 BP and 6,000 BP. A considerable number of aboriginal midden sites have been found, especially on Peron Peninsula and Dirk Hartog Island which provide evidence of some of the foods gathered from the waters and nearby land areas.[1]

The heritage–listed area had a population of fewer than 1,000 people as at the 2011 census and a coastline of over 1,500 kilometres (930 mi). The half-dozen small communities making up this population occupy less than 1% of the total area.

The bay itself covers an area of 1,300,000 hectares (3,200,000 acres), with an average depth of 9 metres (30 ft).[1] It is divided by shallow banks and has many peninsulas and islands. The coastline is over 1,500 kilometres (930 mi) long. There are about 300 kilometres (190 mi) of limestone cliffs overlooking the bay.[6] One spectacular segment of cliffs is known as the Zuytdorp Cliffs. The bay is located in the transition zone between three major climatic regions and between two major botanical provinces.

Dirk Hartog Island is of historical significance due to landings upon it by early explorers. In 1616, Dirk Hartog landed at Inscription Point on the north end of the island and marked his discovery with a pewter plate, inscribed with the date and nailed to a post. This plate was then replaced by Willem de Vlamingh and returned to Holland. It is now kept in the National Museum of Holland. There is a replica in the Shark Bay Discovery Centre in Denham.

Bernier and Dorre islands in the north-west corner of the heritage area are among the last-remaining habitats of Australian mammals threatened with extinction.[citation needed] They are used, with numerous other smaller islands throughout the marine park, to release threatened species that are being bred at Project Eden in François Peron National Park. These islands are free of feral non-native animals which might predate the threatened species, and so provide a safe haven of pristine environment on which to restore species that are threatened on the mainland.

Shark Bay has the largest known area of seagrass, with seagrass meadows covering over 480,000 hectares (1,200,000 acres) of the bay.[6] It includes the 103,000-hectare (250,000-acre) Wooramel Seagrass Bank, the largest seagrass bank in the world.[4] Shark Bay also contains the largest number of seagrass species ever recorded in one place; twelve species have been found, with up to nine occurring together in some places. The seagrasses are a vital part of the complex environment of the bay. Over thousands of years, sediment and shell fragments have accumulated in the seagrasses to form vast expanses of seagrass beds. This has raised the sea floor, making the bay shallower. Seagrasses are the basis of the food chain in Shark Bay, providing home and shelter to various marine species and attracting the dugong population.

In Shark Bay's hot, dry climate, evaporation greatly exceeds the annual precipitation rate. Thus, the seawater in the shallow bays becomes very salt-concentrated, or 'hypersaline'. Seagrasses also restrict the tidal flow of waters through the bay area, preventing the ocean tides from diluting the sea water. The water of the bay is 1.5 to 2 times more salty than the surrounding ocean waters.

Based on growth rate it is believed that about 1,000 years ago cyanobacteria (blue-green algae) began building up stromatolites in Hamelin Pool at the Hamelin Station reserve in the southern part of the bay.[7][8] These structures are modern equivalents of the earliest signs of life on Earth, with fossilized stromatolites being found dating from 3.5 billion years ago at North Pole near Marble Bar, in Western Australia, and are considered the longest continuing biological lineage.[6] They were first identified in 1956 at Hamelin Pool as a living species[dubious – discuss], before that only being known in the fossil record. Hamelin Pool contains the most diverse and abundant examples of living stromatolite forms in the world. Other occurrences are found at Lake Clifton near Mandurah and Lake Thetis near Cervantes.[4] It is hypothesized that some stromatolites contain a new form of chlorophyll, chlorophyll f.[9]

^Agreement between the state of Western Australia and the Commonwealth of Australia on administrative arrangements for the Shark Bay World Heritage Property in Western Australia. WA Department of Conservation and Land Management. Perth, W.A.: Government of Western Australia. 12 September 1997.